1. Field of the Invention
This invention relates generally to the field of optical instruments. More particularly, the invention is directed to an extended wavelength range light source in which a switch is used to select light generated by one of multiple tunable lasers with different tuning ranges.
2. Background of the Related Art
Conventional grating based optical spectrum analyzers (OSA) do not provide sufficient wavelength resolution for future Dense Wavelength Division Multiplexed (DWDM) communication systems. The wavelength resolution provided by current grating based OSA""s is between 0.05 nm to 10 nm, whereas the required/preferred resolution for DWDM communication systems is much higher. The demand for better wavelength resolution for DWDM communication systems is driven by several factors. For example, with channel spacing ranging from 25 GHz to 50 GHz, adequate wavelength resolution is required to support both the signal spectra and the modulated spectra. Furthermore, a higher wavelength resolution improves the ability to resolve the spectral bandwidth, which includes the spectral side bands.
To address these problems, a proposed solution is that future OSAs will be based on coherent optical heterodyne spectrum analysis. A key component of this measurement technology is that a wavelength-tunable optical source, such as a laser, is used as a local oscillator (LO). One limitation of a tunable laser is that its wavelength tuning range is limited to a range of about 30-200 nm, which is a relatively small range compared to the normal spectral range for most OSAs. This small spectral range poses a problem to increasing the use and acceptance of the coherent heterodyne OSAs.
Therefore, it is a general objective of the invention to alleviate the problems and shortcomings identified above.
These and other objectives are achieved by providing in one aspect of the present invention a light source for an optical instrument. The light source includes wavelength-tunable optical sources that generate optical signals. Each of the optical sources has a distinct wavelength-tunable range that differs from the wavelength-tunable ranges of the other optical sources. The light source additionally includes a switch connected to each of the optical sources. The switch is configured to select any one of the optical sources and to transmit the optical signal from the selected optical source. The optical instrument may be a coherent heterodyne optical spectrum analyzer (OSA) that also includes a coherent heterodyne optical receiver that receives the optical signal from optical source selected by the switch and an external optical signal that is to be analyzed.
In another aspect of the invention, the optical instrument includes optical sources such that the distinct wavelength-tunable ranges of the optical sources at least partially overlap with at least one other of the optical sources.
In a further aspect of the invention, the distinct wavelength-tunable range of each of the optical sources is 30-200 nm.
In another aspect of the invention, the optical source is made using semiconductor materials and the tunable range of the optical sources, such as semiconductor lasers, is varied by varying the composition of the semiconductor materials.
In another aspect of the invention, the tunable optical sources are provided by using lasers as local oscillators.
In a further aspect of the invention, the optical sources are provided by using vertical cavity surface emitting lasers (VCSEL) with micro-machined mirrors so that the positions of the mirrors is adjustable to provide the tuning.
In another aspect of the invention, the switch includes a Nxc3x971 optical switch which outputs one optical signal from any one of N optical inputs.
In another aspect of the invention, the switch functionality is provided by a WDM combiner.
A further aspect of the present invention provides a method of extending the range of a light source for an optical instrument by generating optical signals each having a distinct wavelength-tunable range, selecting one of the optical signals and transmitting the selected one of the optical signals to the optical instrument.